Have you ever noticed that the mile markers and your odometer reading are off? A difference of tenth of a mile or tow in a 10 mile stretch is not unusual. Over or undersized tires will cause both your odometer and speedometer to read differently.
New tires, with full tread, make fewer revolutions per mile than do bald tires. What happens to all that rubber that's worn off millions of tires? It accumulates alongside our nation's highways. Some of this rubber was scrubbed off because the wheels are out of alignment.
Imagine a car, driven about 12,000 miles a year, going down the road with wheels misaligned by just .17 inches. The driver must constantly tug at the wheel to keep the car going straight. In effect, the tires are being dragged sideways for the equivalent of 68 miles over the course of a year. This condition, along with under-inflation, increases rolling resistance. The end result being tires wasted away, fuel economy plummeting as gas goes out the exhaust and one or more tires needing replacement prematurely.
How do you know if your tires are wearing too quickly or unevenly? Steering irregularities, such as pulling in one direction or wandering, indicate either one tire under-inflated or misaligned wheels. Visit a certified repair facility to have your alignment checked if you are concerned that you have this problem.